This invention refers to refractory compositions, particularly compositions suitable for ramming, casting, and gunning.
Such compositions are well known in the art, for example as disclosed in U.S. Pat. No. 3,030,216, which mentions refractory compositions containing fine magnesia, magnesium sulfate, and an organic acid such as acetic, citric, or tartaric, and also mentions the possibility of adding boron compounds to inhibit swelling due to hydration.
However, such prior art compositions have problems, for example the tendency to explode when heated. Although boron compounds have long been added to such compositions to inhibit explosion, they are not always completely successful and there is a continuing search for products which will resist explosion at faster and faster heating rates.
One successful prior art composition is described in U.S. Pat. No. 2,702,751. There the principal bonding agent is chromic acid or a soluble chromate or other chromium compound. However, in recent years there has been increasing concern over the use of potentially hazardous materials such as chromium-containing compounds, especially those which produce Cr.sup.+6 ions when dissolved in water, and a search has been made for substitute bonds which can be used to make a product having equivalent properties but free of such hazardous substances. U.S. Pat. No. 3,333,972 concerns the use of citric acid in magnesia-containing compositions and mentions the possibility of also including magnesium sulfate and boric acid in such compositions.
The use of sodium gluconate is known in cement compositions, either as a set accelerator, as in U.S. Pat. No. 3,782,984, where it is used in conjunction with alkali metal acid carbonate and alkali metal silicate; or as a cement retarder, as in U.S. Pat. No. 3,351,478, where it is used in conjunction with a soluble sulfate such as sodium, potassium, or ammonium sulfate; or U.S. Pat. No. 3,856,541, where it is used in conjunction with boric acid or a water soluble salt thereof.
Accordingly, the present invention solves the problem of producing an explosion resistant-refractory suitable for ramming, casting, or gunning, and bonded with substances free of soluble chromium.